WHEN did the coronavirus first reach Europe and the US?
No cases were reported outside China until January 2020, but a published on 10 September claims that cases in the US began to rise by 22 December. Many people there and in Europe suspect they had coronavirus around this time. Yet overall, the evidence suggests there were few cases outside China this early on.
Covid-19 was first recognised as a new disease in Wuhan, China, over the course of December. On 13 January, the first case outside China was reported in Thailand. On 21 January, the US reported its first case and on 24 January, France reported three, the first in Europe.
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This, at least, is what was known at the time. But it can take up to two weeks for covid-19 symptoms to appear and many infected people don鈥檛 have symptoms at all.
In addition, when countries did start testing, many initially limited it to people who had come from China recently. If the virus had already begun spreading, any early local cases would have been missed. 鈥淚t is certain there were many cases we did not see,鈥� says Lauren Ancel Meyers at the University of Texas at Austin.
But how many and how soon? One team says it found viral RNA in , Spain, as early as March 2019, but others have dismissed this. 鈥淚t is highly likely to be contamination,鈥� says Kristian Andersen at the Scripps Research Institute in California.
The 10 September study is based on the number of people going to a group of hospitals and clinics in the Los Angeles area with a cough, but just because people had symptoms resembling covid-19 doesn鈥檛 mean they had it. 鈥淚t鈥檚 extremely unlikely,鈥� says Dominik Mertz at McMaster University in Canada. 鈥淚 think we can be pretty sure it was something else.鈥�
In fact, it is very unlikely that anyone was infected by the virus before November. Several teams tracing its evolution by looking at changes in RNA of samples of the virus sequenced so far have all concluded that the pandemic strain emerged around November.
鈥淲hile it鈥檚 possible lots of people in the West had covid-19 then, it is more likely it was another virus鈥�
On the flip side, this does mean that people in Italy may have been infected by 18 December, , and that a man in France could have been infected as early as 14 December, as testing of stored hospital samples suggests.
Based on two studies that found missed cases by testing stored hospital samples in Wuhan and Seattle, Meyers鈥檚 team that there could have been 10,000 cases in Wuhan by 23 January when only 400 had been detected, and 9000 in Seattle by 9 March, when only 245 had been reported.
However, even if Meyers鈥檚 estimates are right, it doesn鈥檛 mean lots of people outside Wuhan had the coronavirus as early as December. 鈥淲hile it is possible, it鈥檚 much more likely they had some other respiratory virus,鈥� says Meyers.
